Force‐length characteristics of the in vivo human gastrocnemius muscle

Abstract

In this study, the force-length characteristics of the in vivo medial (GM) and lateral (GL) heads of the human gastrocnemius muscle were estimated from measurements in eight healthy male subjects. This involved: 1) dynamometry-based measurements of the moment generated during maximal isometric plantar flexion; 2) ultrasound-based measurements of fascicular length and pennation angle; and 3) ultrasound-based calculations of moment arm lengths. All measurements were taken over the ankle angle range from 20 degrees of dorsiflexion to 30 degrees of plantar flexion. Tendon forces were calculated by dividing the moments recorded by the muscle moment arm lengths, and fascicular forces were calculated by dividing the tendon forces estimated by the cosine of pennation angle. In the transition from 30 degrees of plantar flexion to 20 degrees of dorsiflexion, the GM muscle fascicular length and force increased linearly from 24 to 39 mm and from 222 to 931 N, respectively. Over the same ankle angle range, the GL muscle fascicular length and force increased linearly from 30 to 47 mm and from 139 to 393 N, respectively. Estimates of the sarcomeric lengths corresponding to the fascicular lengths measured indicated that the two muscles operated in the range 1.4-2.2 microm, below the optimal length region for force generation according to the cross-bridge mechanism of contraction. These results indicate that the force-length relation of the in vivo human gastrocnemius muscle is limited to the ascending limb of the bell-shaped force-length curve obtained from experiments on isolated material.

Can pennation angles be predicted from EMGs for the primary ankle plantar and dorsiflexors during isometric contractions?

“…This is in stark contrast to findings by Kawakami et al (1998) who reported in vivo ultrasound pennation angles of 31±6° for the LG at MVC, considerably different than the smaller values used by Bogey et al, (2005). The average pennation angle for the male subjects in our study was 22°; identical to the in vivo value reported by Maganaris (2003). Differences between cadaver and in vivo measures of muscle architecture for the triceps surae were studied by Martin and colleagues (2001).…”

“…Muscle fiber length and pennation angle changes with muscle contraction intensity (Maganaris et al, 1998;Maganaris, 2003;Narici et al, 1996). Contractile effort is reflected in the magnitude of the electromyogram (Buchanan et al, 2004), and therefore the EMG signal may be a predictor of fiber length and pennation angle change.…”

“…Muscles with large pennation angles such as the soleus allow more fibers to be arranged in parallel within a given cross sectional area, thereby increasing a muscle's force generating potential. Fiber pennation angle varies with muscle contraction intensity and fiber length (Maganaris et al, 1998;Maganaris, 2003;Narici et al, 1996), and thus such changes should be considered when using musculoskeletal models to estimate muscle force.…”

Direct comparison of in vivo Achilles tendon moment arms obtained from ultrasound and MR scans

“…One method used to estimate muscle forces is calculation of the ratio of the muscular moment about a joint and the moment arm of the muscle or tendon of interest. A number of techniques can be used to obtain muscle moment arms, including cadaver dissection (6,7,11,27), magnetic resonance (MR) imaging (16,26), and ultrasound imaging (9,(12)(13)(14).…”

Influência de posições do joelho no torque e atividade mioelétrica do tríceps sural na flexão plantar isométrica máxima

“…Isto se dá pelo menor comprimento da bra do GNM, que implica em uma menor amplitude efetiva de produção de torque máximo 23 . O GNL, por outro lado, com bras mais longas, poderia manter níveis su cientes de torque por uma maior variação de comprimento da bra.…”